An electric power steering system (EPS) measures signals including torsion bar torque and motor velocity. These signals may be used to devise control algorithms and an architecture that provide desired steering feel, while maintaining system stability. FIG. 1 illustrates an EPS control architecture 20 consisting of two control loops, a torque loop based mainly on measured torque, and a velocity loop mainly based on measured motor velocity. In practical application, both loops may use other EPS and vehicle signals such as assist command, vehicle speed etc. A velocity controller 22 controls the velocity loop and a torque controller 24 controls a torque loop. The velocity controller 22 provides a part of motor torque signal for a motor of the electric power steering system 30, and the torque controller 24 provides motor torque signal for the motor. The motor velocity signal and the motor torque signal are joined at summation block 28, and a summed signal is provided to the motor of the electric power steering system 30. The motor represents motor control architecture as well as electric motor dynamics. The motor generates a torque command that acts on components within the electric power steering system 30.
Frequency-dependent damping, motor velocity damping and inertia compensation are examples of the functions that act primarily in the velocity loop. Inertia compensation, for example, may compensate for the motor inertia, but higher gains may lead to a decrease in the stability margins of the steering system.